Increased interleukin-4 production by atopic mononuclear leukocytes correlates with increased cyclic adenosine monophosphate-phosphodiesterase activity and is reversible by phosphodiesterase inhibition

Targeted Systemic Therapies for Adults with Atopic Dermatitis: Selecting from Biologics and JAK Inhibitors

Therapeutic options for people with moderate or severe atopic dermatitis refractory to topical therapy have rapidly expanded in recent years. These new targeted immunomodulatory agents-biologics and Janus kinase (JAK) inhibitors-have each demonstrated high levels of efficacy and acceptable safety in mostly placebo-controlled clinical trials for atopic dermatitis, but there is no universally applicable algorithm to help choose between them for a given patient. Hence, patients and physicians should utilize shared decision making, discussing efficacy, safety, mode of delivery, monitoring, costs, speed of onset, and other factors to reach individualized treatment decisions. In this review, we try to aid shared decision making by summarizing the efficacy, safety, and monitoring of biologics and oral JAK inhibitors for adults with atopic dermatitis. Network meta-analyses suggest that higher doses of abrocitinib and upadacitinib are more effective than biologics. They also show that, among biologics, dupilumab is likely more effective than tralokinumab and lebrikizumab. Biologics are generally considered safer than JAK inhibitors, although concerns about JAK inhibitors are mainly extrapolated from older generation JAK inhibitors used in higher-risk populations. We also outline evidence and considerations for choosing and using systemic immunomodulatory treatments for special populations including pregnant individuals, those with human immunodeficiency virus (HIV), hepatitis B and C, end stage kidney disease, and older adults.

Subgroup Analysis of Crisaborole for Mild-to-Moderate Atopic Dermatitis in Children Aged 2 to < 18 Years

OBJECTIVES

This post hoc analysis of pooled data from two phase III studies (AD-301: NCT02118766; AD-302: NCT02118792) explored the efficacy and safety of crisaborole ointment, 2%, a nonsteroidal phosphodiesterase 4 inhibitor, for the treatment of mild-to-moderate atopic dermatitis (AD) in pediatric patients (aged 2 to < 18 years) only, stratified by baseline characteristics.

METHODS

Pediatric patients with mild or moderate AD per Investigator's Static Global Assessment (ISGA) and percentage of treatable body surface area (%BSA) ≥ 5 at baseline were assessed. Crisaborole or vehicle (2:1 randomization ratio) was applied twice daily for 28 days. Of the 1313 pediatric patients included in this study, 874 received crisaborole and 439 received vehicle. ISGA success was defined as clear (0) or almost clear (1) with ≥ 2-grade improvement from baseline. Efficacy and safety were stratified by age group, sex, baseline ISGA, baseline %BSA per published severity strata, and prior AD therapy.

RESULTS

Overall, the proportions of crisaborole-treated and vehicle-treated pediatric patients with ISGA success at week 4 were 32.5 and 21.5%, respectively. ISGA success rates at day 29 (week 4) were generally higher in crisaborole-treated (21.9-38.1%) than vehicle-treated (15.7-26.9%) patients across subgroups. Rates of treatment-related application site pain were 2.4-10.1% for crisaborole-treated patients and 0.6-2.2% for vehicle-treated patients across subgroups. No new safety concerns were noted in any patient subgroup.

CONCLUSION

Crisaborole improved global disease severity and was reasonably well tolerated across all pediatric baseline characteristic subgroups. Application site discomfort was greater with crisaborole than with vehicle, but few patients discontinued treatment.

GOV REGISTRATION NUMBERS

NCT02118766; NCT02118792 (registration date: April 21, 2014).

Phosphodiesterase 4B: Master Regulator of Brain Signaling

Phosphodiesterases (PDEs) are the only superfamily of enzymes that have the ability to break down cyclic nucleotides and, as such, they have a pivotal role in neurological disease and brain development. PDEs have a modular structure that allows targeting of individual isoforms to discrete brain locations and it is often the location of a PDE that shapes its cellular function. Many of the eleven different families of PDEs have been associated with specific diseases. However, we evaluate the evidence, which suggests the activity from a sub-family of the PDE4 family, namely PDE4B, underpins a range of important functions in the brain that positions the PDE4B enzymes as a therapeutic target for a diverse collection of indications, such as, schizophrenia, neuroinflammation, and cognitive function.

Development and validation of a simple method for the extraction and quantification of crisaborole in skin layers

Crisaborole is a boron compound recently approved by the US Food and Drug Administration as a 2% ointment for the treatment of mild to moderate atopic dermatitis. This work describes a simple method for the quantification of the drug in the skin layers at the end of in-vitro permeation experiments. Chromatographic separation was carried out on a reverse-phase C₁₈ column using a mixture of trifluoroacetic acid 0.05%-acetonitrile (55:45, v/v) as mobile phase, pumped at 1 ml/min. Column temperature was 35°C and UV detection was performed at 250 nm. The method was linear in the range of concentration from 0.06 to 6 μg/ml (R²  = 1) and was selective, precise and accurate. Depending on the solvent used, the LOQ ranged from 0.014 to 0.030 μg/ml and the LOD from 0.005 to 0.010 μg/ml. The extraction from all the skin layers was quantitative. The developed method was successfully tested in an in-vitro permeation study, proving to be an effective tool in the development of new formulations containing crisaborole.

Adult atopic dermatitis: new and emerging therapies

INTRODUCTION

Adult atopic dermatitis (AD) is very difficult to manage. Indeed, AD in adults is frequently refractory to topical treatment, especially with regards to the persistent form. Therefore, long-term treatment with oral immunosuppressive therapy is often required to control the burden of the disease, prevent flare-ups and achieve better patient quality of life outcomes. Areas covered: In the last decade the better understanding of AD pathogenesis has been used to improve treatment strategies with many emerging therapeutics options. Epidermal barrier impairment often plays the initial role in the initiation of the disease. Moreover, T helper 2 cytokines interleukin (IL)-4 and IL-13 and their downstream effects are prominent in AD, with pleiotropic effects on the innate and adaptive immune system. Targeting these cells, their products or receptors appears to be a reasonable therapeutic strategy. Expert commentary: In the next years, many therapeutic options for adult AD will be available. Clinical trials showed that JAK inhibitors, PDE-4 inhibitors and monoclonal antibodies against some IL (IL-4, IL 13, IL-17, IL-22, IL-31) seem to be the most promising drugs, but dermatologists will have to evaluate their effectiveness and safety in clinical practice.

Vascular pattern of the palms--a clinical feature of atopic skin diathesis

BACKGROUND

Atopic skin diathesis is a clinical term to describe skin atopics with previous, present or future atopic eczema/dermatitis syndrome (AEDS). In clinical practice, an unequivocal assessment of atopic skin diathesis in non-eczematous patients may be difficult. The majority of the known clinical features included in diagnostic scores are characteristic, but not specific markers of atopy. Especially, the vasoreactivity of atopic skin is disturbed. This is manifested by white dermographism, an irregular vascular response to thermal stimuli, and paradoxic skin reactions to histamine, cholinergic agents, and nicotinates.

OBJECTIVE

The aims of our study were to investigate the clinical morphology of palmar vascular reactions in skin atopic and non-atopic individuals, and to determine whether this abnormal vascular reaction is more pronounced in skin atopic individuals.

METHODS

Forty persons, 20 of them skin atopics, assessed by the Erlangen Atopy Score and an elevated serum IgE level (>150 U/ml), were included in a prospective single-centre study. Standardized digital photographs of the palms were presented in a blinded manner to five dermatologists in random order by means of the computerized imaging analysis system KS400 3.0.

RESULTS

Evaluation of the original rgb (red, green, blue) color images and modified gray-level images showed that a pronounced reticular pattern of erythema of the palms was significantly (P < 0.0001) more common in skin atopics (72% and 69.6%, respectively).

CONCLUSION

The gross vascular pattern of the palm might be an additional diagnostic feature of atopy, and further studies are needed to establish its exact prevalence.

Early up-regulation of Th2 cytokines and late surge of Th1 cytokines in an atopic dermatitis model

We investigated cytokine profiles in interleukin (IL)-4 transgenic (Tg) mice with a skin inflammatory disease resembling human atopic dermatitis. cDNA microarray revealed that the mRNAs encoding IL-1beta, IL-2, IL-3, IL-4, IL-5, IL-6, IL-10, IL-12p40, IL-13, tumour necrosis factor (TNF)-alpha, TNF-beta and interferon (IFN)-gamma were up-regulated in the skin of late lesion Tg mice and to a lesser degree in non-lesion Tg mice when compared to those of non-Tg mice. Real time reverse transcription-polymerase chain reaction (RT-PCR) analyses indicated that the cDNA copy numbers of IL-1beta, IL-4, IL-6, IL-10, TNF-alpha and IFN-gamma from the skin of late, early and non-lesions increased significantly compared to non-Tg mice. IL-2 and IL-12p40 cDNA copy numbers were increased significantly in early, but not late, lesions. Interestingly, IL-1beta, IL-3, IL-4, IL-5, IL-6, IL-10, IL-13, TNF-alpha, and IFN-gamma cDNAs were increased significantly the skin of before-onset and/or non-lesion mice. Flow cytometry analyses demonstrated an increased percentage of keratinocytes producing IL-4 as the disease progressed. The percentage of IL-2, IL-4, IL-10 and IFN-gamma-producing T cells and IL-12-producing antigen-presenting cells in skin-draining lymph nodes and inflammatory skin also increased, particularly in mice with late lesion. These results suggest that disease induction is primarily triggered by Th2 cytokines and that Th1, Th2 and non-Th proinflammatory cytokines are all involved in the disease process.

Upregulation of phosphodiesterase-4 in the lung of allergic rats

Inhibitors of phosphodiesterase-4 (PDE4) are efficacious for allergic asthma in animal models and have shown some efficacy in human asthma. Regulation of PDE4 in allergy and asthma has been widely investigated in blood leukocytes, with discrepant results. This study investigated PDE4 regulation in the lung in a rat model of allergic asthma. Ovalbumin sensitization and challenge significantly increased pulmonary resistance and lung interleukin (IL)-4 production. The increases in pulmonary resistance and IL-4 production were both suppressed by the PDE4-selective inhibitor rolipram or the corticosteroid drug dexamethasone. Furthermore, cAMP-PDE enzyme activity in the lung was also significantly increased by the sensitization and challenge. mRNA analysis confirmed that PDE4 gene expression was increased in the lung of the allergic rats. A highly significant correlation was observed between the increases in PDE activity and IL-4 production. Our data suggest, for the first time, that PDE4 may be upregulated in the lung and play a role in the pathogenesis of allergic asthma.

Biochemical and functional assessment of equine lymphocyte phosphodiesterases and protein kinase C

Lymphocytes play an important role in allergic inflammation and have been implicated in the pathogenesis of equine allergic skin and respiratory disease. Targeting intracellular signalling pathways in human lymphocytes has demonstrated a role for both phosphodiesterase and protein kinase C in cell activation. The aim of this study was to measure total cyclic nucleotide hydrolysing phosphodiesterase activity and to identify the phosphodiesterase and protein kinase C isoenzymes present in equine lymphocytes. The functional significance of these isoenzymes was then investigated by examining their role in peripheral blood mononuclear cell proliferation using isoenzyme selective inhibitors. Total cyclic adenosine monophosphate hydrolysing phosphodiesterase activity was double that of cyclic guanosine monophosphate (30+/-2 pmol/min mg versus 16+/-3 pmol/min mg for cyclic adenosine and cyclic guanosine monophosphate phosphodiesterase activity, respectively). Evidence for the presence of PDE1, 3, 4 and 5 was obtained and PKCalpha, beta, delta, eta, iota, theta and zeta were identified. Selective inhibitors of PDE4, PKCdelta and conventional PKCs alpha and beta caused significant inhibition of mitogen-induced peripheral blood mononuclear cell proliferation. This study demonstrates a functional role for specific signalling isoenzymes and suggests that, in the context of allergic inflammation, targeting inflammatory cells involved in disease pathogenesis with relevant isoenzyme inhibitors may have therapeutic potential.

Interleukin-10 therapy--review of a new approach

Interleukin (IL)-10 is an important immunoregulatory cytokine produced by many cell populations. Its main biological function seems to be the limitation and termination of inflammatory responses and the regulation of differentiation and proliferation of several immune cells such as T cells, B cells, natural killer cells, antigen-presenting cells, mast cells, and granulocytes. However, very recent data suggest IL-10 also mediates immunostimulatory properties that help to eliminate infectious and noninfectious particles with limited inflammation. Numerous investigations, including expression analyses in patients, in vitro and animal experiments suggest a major impact of IL-10 in inflammatory, malignant, and autoimmune diseases. So IL-10 overexpression was found in certain tumors as melanoma and several lymphomas and is considered to promote further tumor development. Systemic IL-10 release is a powerful tool of the central nervous system to prevent hyperinflammatory processes by activation of the neuro-endocrine axis following acute stress reactions. In contrast, a relative IL-10 deficiency has been observed and is regarded to be of pathophysiological relevance in certain inflammatory disorders characterized by a type 1 cytokine pattern such as psoriasis. Recombinant human IL-10 has been produced and is currently being tested in clinical trials. This includes rheumatoid arthritis, inflammatory bowel disease, psoriasis, organ transplantation, and chronic hepatitis C. The results are heterogeneous. They give new insight into the immunobiology of IL-10 and suggest that the IL-10/IL-10 receptor system may become a new therapeutic target.

Randomized comparison of the type 4 phosphodiesterase inhibitor cipamfylline cream, cream vehicle and hydrocortisone 17-butyrate cream for the treatment of atopic dermatitis

BACKGROUND

Therapeutic options to treat atopic dermatitis are limited. Leukocytes from atopic patients have an abnormally high activity of cyclic adenosine monophosphate (AMP)-phosphodiesterase (PDE), which can be normalized in vitro by PDE inhibitors. Cipamfylline is a new potent and selective inhibitor of PDE-4.

OBJECTIVES

To compare the efficacy and safety of up to 14 days' topical treatment with cipamfylline (0.15%) cream with vehicle and with hydrocortisone 17-butyrate (0.1%) cream.

PATIENTS AND METHODS

International, multicentre, prospective, randomized double-blind, left-right studies of cipamfylline vs. vehicle and cipamfylline vs. hydrocortisone 17-butyrate in adult patients with stable symmetrical atopic dermatitis on the arms.

RESULTS

Both cipamfylline and hydrocortisone 17-butyrate reduced the Total Severity Score significantly (P < 0.001). The reduction with cipamfylline was significantly greater than that with vehicle (difference vehicle-cipamfylline 1.67 95% confidence interval (CI) 1.06, 2.28; P < 0.001) and was significantly less than with hydrocortisone 17-butyrate (difference hydrocortisone-cipamfylline -2.10 95% CI -2.93, -1.27; P < 0.001). Investigator and patient assessments of the overall treatment response showed a similar picture.

CONCLUSIONS

Cipamfylline cream is significantly more effective than vehicle, but significantly less effective than hydrocortisone 17-butyrate cream in the treatment of atopic dermatitis.

The antidepressant and antiinflammatory effects of rolipram in the central nervous system

Rolipram is a selective inhibitor of phosphodiesterases (PDE) IV, especially of the subtype PDE IVB. These phosphodiesterases are responsible for hydrolysis of the cyclic nucleotides cAMP and cGMP, particularly in nerve and immune cells. Consequences of rolipram-induced elevation of intracellular cAMP are increased synthesis and release of norepinephrine, which enhance central noradrenergic transmission, and suppress expression of proinflammatory cytokines and other mediators of inflammation. In humans and animals rolipram produces thereby a variety of biological effects. These effects include attenuation of endogenous depression and inflammation in the central nervous system (CNS), both effects are of potential clinical relevance. There are some discrepancies between in vitro and in vivo effects of rolipram, as well as between results obtained in animal models and clinical studies. The clinical use of rolipram is limited because of its behavioral and other side effects. Newly developed selective PDE IV inhibitors with presumably higher potency and lower toxicity are currently under investigation.

Differential effect of phosphodiesterase inhibitors on IL-13 release from peripheral blood mononuclear cells

Increased cyclic AMP (cAMP)-phosphodiesterase (PDE) activity in peripheral blood leucocytes is associated with the immunological inflammation that characterizes allergic diseases, such as atopic dermatitis and allergic rhinitis. Recently, it has been found that IL-13 has similar biological functions to IL-4. The aim of this study was to investigate the possible involvement of cAMP-PDE activity on IL-13 release from peripheral blood mononuclears cells (PBMC) from atopic asthma patients. Phytohaemagglutinin (PHA)-induced IL-13 release from PBMC was concentration-dependently inhibited by rolipram, a type 4 PDE inhibitor, as well as by dibutyryl cAMP, a membrane-permeant cAMP analogue. However, theophylline, a non-specific PDE inhibitor, and cilostazol, a type 3 PDE inhibitor, failed to inhibit IL-13 release. The inhibitory effect of rolipram was enhanced by the addition of forskolin (10(-4) m), an adenylyl cyclase stimulator. PHA itself did not alter the intracellular cAMP level. Rolipram concentration-dependently increased cAMP level in PHA-stimulated PBMC, and this increase was synergistically facilitated by the addition of forskolin (10(-4) m). These results suggest that type 4 PDE inhibitors, alone or synergistically in combination with forskolin, inhibit PHA-induced IL-13 release from PBMC of atopic asthma patients by elevating intracellular cAMP concentrations. These inhibitors have the potential to exert an anti-inflammatory effect by inhibiting IL-13 production in allergic diseases such as atopic asthma.

Cyclic nucleotide phosphodiesterases

Cyclic nucleotide second messengers (cAMP and cGMP) play a central role in signal transduction and regulation of physiologic responses. Their intracellular levels are controlled by the complex superfamily of cyclic nucleotide phosphodiesterase (PDE) enzymes. Continuing advances in our understanding of the molecular pharmacology of these enzymes has led to the development of selective inhibitors as therapeutic agents for disease states ranging from cancer and heart failure to depression and sexual dysfunction. Several PDE types have been identified as therapeutic targets for immune/inflammatory diseases. This article briefly reviews the available in vitro, preclinical, and clinical data supporting the potential for selective PDE inhibitors as immunomodulatory agents.

Prevention by theophylline of beta-2-receptor down regulation in healthy subjects

Adrenergic down-regulation can occur rapidly in many tissues. Therefore beta 2-agonists might have a rapidly decreasing effect in time, which is a potential problem for the treatment of bronchial asthma. This in vivo study tested the hypothesis that theophyline can prevent adrenergic down-regulation. A randomised, double blind, placebo-controlled cross-over study was performed in eight healthy subjects. Terbutaline concentration-effect relationships were studied before and after one week of dosing of terbutaline, with or without theophylline. Slow-release terbutaline 5 mg daily was administered for 7 days in combination with either placebo or slow-release theophylline. Concentration-effect relationships of terbutaline after a single subcutaneous injection were studied before and after the 7 day terbutaline treatment. Eosinopenia and hypokalemia were the systemic effect parameters. Terbutaline concentration-time courses were described with a two-compartment model and those of theophylline with a polynomial equation. A hypothetical effect compartment model was applied to link terbutaline plasma concentration via an Emax model to the studied effects. The interaction of theophylline and terbutaline was described with a non-competitive pharmacodynamic model. After one week of oral terbutaline, the mean EC50 (ng/L) of terbutaline increased for the eosinopenia from 1.87 +/- 1.66 to 3.78 +/- 2.18 (+102%) (p = 0.012) with placebo, and to 2.73 +/- 1.99 (+46%) (p = 0.025) with theophylline; for the hypokalemia the EC50 increased from 4.70 +/- 2.91 to 8.52 +/- 7.26 (+81%) (p = 0.012) with placebo, and to 5.64 + 2.59 (+20%) (p = 0.16) with theophylline. The results indicate that the non-specific phosphodiesterase inhibitor theophylline can prevent terbutaline-induced adrenergic down-regulation to a substantial degree.

Phosphodiesterase 4 inhibitors and the treatment of asthma: where are we now and where do we go from here?

Research conducted over the last 20 years has established that inflammation of the airways is central to the airway dysfunction that characterises asthma. Typically, the airway wall is infiltrated by a variety of cells including mast cells, eosinophils and T lymphocytes, which have deviated towards a T(H)2 phenotype. Together, these cells release a plethora of mediators including interleukin (IL)-4, IL-5, granulocyte/macrophage colony-stimulating factor and eotaxin which ultimately cause the histopathology and symptoms of asthma. Glucocorticosteroids are the only drugs currently available that effectively impact upon this inflammation and resolve, to a greater or lesser extent, compromised lung function. However, steroids are nonselective and generally unsuitable for paediatric use. New drugs are clearly required. One group of potential therapeutic agents for asthma are inhibitors of cyclic AMP-specific phosphodiesterase (PDE), of which theophylline may be considered a prototype. It is now known that PDE is a generic term which refers to at least 11 distinct enzyme families that hydrolyse cAMP and/or cGMP. Over the last decade, inhibitors of PDE4 (a cAMP-specific family that negatively regulates the function of almost all pro-inflammatory and immune cells, and exerts widespread anti-inflammatory activity in animal models of asthma) have been developed with the view to reducing the adverse effects profile associated with non-selective inhibitors such as theophylline. Such is the optimism regarding PDE4 as a viable therapeutic target that more than 100 PDE4 inhibitor patent applications have been filed since 1996 by 13 major pharmaceutical companies. This article reviews the progress of PDE4 inhibitors as anti-inflammatory agents, and identifies problems that have been encountered by the pharmaceutical industry in the clinical development of these drugs and what strategies are being considered to overcome them.

Therapeutic potential of phosphodiesterase-4 and -3 inhibitors in Th1-mediated autoimmune diseases

Phosphodiesterase-4 (PDE4) inhibitors have the potential to modulate immune responses from the Th1 toward the Th2 phenotype and are considered candidate therapies for Th1-mediated autoimmune disorders. However, depending on the model and cell types employed, studies of atopic individuals have come to the opposite conclusion, i.e., that PDE inhibitors may be beneficial in asthma. Using in vitro immunopharmacologic techniques we analyzed the effects of PDE4 and PDE3 inhibitors on human immune cells to address these discrepancies and broaden our understanding of their mechanism of action. Our results indicate that PDE inhibitors have complex inhibitory effects within in vivo achievable concentration ranges on Th1-mediated immunity, whereas Th2-mediated responses are mostly unaffected or enhanced. The Th2 skewing of the developing immune response is explained by the effects of PDE inhibitors on several factors contributing to T cell priming: the cytokine milieu; the type of costimulatory signal, i.e., up-regulation of CD86 and down-regulation of CD80; and the Ag avidity. The combination of PDE4 and PDE3 inhibitors expresses synergistic effects and may broaden the therapeutic window. Finally, we observed a differential sensitivity to PDE inhibition in autoreactive vs foreign Ag-specific T cells and cells derived from multiple sclerosis patients vs those derived from healthy donors. This suggests that PDE inhibition weakens the strength of the T cell stimulus and corrects the underlying disease-associated cytokine skew in T cell-mediated autoimmune disorders. These new findings broaden the understanding of the immunomodulatory actions of PDE inhibitors and underscore their promising drug profile for the treatment of autoimmune disorders.

Mechanisms of deficient interferon-gamma production in atopic diseases

BACKGROUND

The mechanisms responsible for an imbalanced cytokine response in atopic diseases are still not understood. While impaired interferon-gamma (IFN-gamma) production may be the result of a pathological T-cell/antigen-presenting cell (APC) interaction, evidence was provided that the T cell itself may have an intrinsic defect to produce IFN-gamma.

OBJECTIVE

To clarify whether impaired IFN-gamma production by T cells from patients with atopic dermatitis (AD) represents an intrinsic defect in producing IFN-gamma.

METHODS

Effector T cells were generated from CD4+ CD45RA+-naive precursors from patients with AD and healthy control individuals by activation with anti-CD3+ anti-CD28 MoAbs. Following restimulation, IFN-gamma production was measured by ELISA and flow cytometry.

RESULTS

IFN-gamma production by atopic T cells was decreased compared with healthy T cells. IL-12 present at priming or high doses of IL-2 during the culture period, even in the absence of IL-12, completely restored IFN-gamma production. Conversion of naive CD45RA+ to CD45R0+ effector cells did not differ between atopic and healthy donors' T cells.

CONCLUSION

Impaired IFN-gamma production by T cells from atopic individuals is not the result of an intrinsic, genetically fixed, defect to produce sufficient amounts of IFN-gamma. The data provides evidence that correction of an impaired TH1 response in AD may be successful at the precursor T cell level.

Biochemical and immunologic mechanisms in atopic dermatitis: new targets for emerging therapies

The immunologic and pharmacophysiologic features of atopic dermatitis have stimulated research seeking to identify relevant effector cells and mediators that characterize chronic skin inflammation. The theory that unifies the various abnormalities associated with atopic dermatitis suggests that hematopoietic cells carrying abnormal genetic expressions of atopy cause clinical disease once they infiltrate the skin and mucosa. The proposed underlying mechanism may be either abnormalities in cyclic nucleotide regulation of marrow-derived cells or allergenic overstimulation that causes secondary abnormalities. The primacy of one mechanism over the other remains unresolved, but this does not obviate their value in identifying two novel therapeutic targets: phosphodiesterase inhibition and immune-intervention alternatives to corticosteroids. New type IV phosphodiesterase inhibitors are proving promising in topical formulations, as are inhibitors of calcineurin, such as FK506 and SDZ ASM 981, an ascomycin macrolactam derivative that in early clinical research appears to offer the potency of a corticosteroid without its adverse side effects. The promising clinical trial profiles of these new topical agents may result in alternative therapies providing potent anti-inflammatory activity without the adverse effects that limit corticosteroid use.

Cyclic nucleotide phosphodiesterase (PDE) inhibitors and immunomodulation

Intracellular levels of cyclic nucleotide second messengers are regulated predominantly by the complex superfamily of cyclic nucleotide phosphodiesterase (PDE) enzymes. Recent advances in our understanding of the molecular pharmacology of these enzymes has led to their identification as biologic regulators of certain disease states and the development of isozyme-selective inhibitors as potential therapeutic agents. A large body of in vitro and preclinical data suggests the therapeutic utility of PDE4 inhibitors as potent anti-inflammatory agents. Early clinical trials with selective PDE inhibitors substantiate this approach while highlighting pharmacodynamic and toxicologic pitfalls inherent to the inhibition of specific PDE isozymes. This commentary will review our current understanding of PDE inhibitors as immunomodulatory agents.

Staphylococcal toxic shock syndrome toxin-1 inhibits monocyte apoptosis

BACKGROUND

Chronic atopic dermatitis (AD) lesions are associated with colonization by exotoxin-producing Staphylococcus aureus. Evidence suggests that cytokine production in AD, particularly of GM-CSF, prolongs survival of both peripheral blood monocytes and dermal monocyte-macrophages, the predominate inflammatory cell in lesions caused by chronic AD.

OBJECTIVE

We sought to determine whether the staphylococcal exotoxin, toxic shock syndrome toxin-1 (TSST-1), could stimulate prosurvival cytokine production in monocytes and thereby inhibit apoptosis.

METHODS

Cultures of peripheral blood monocytes from normal donors and subjects with AD were incubated with various concentrations of TSST-1, and the incidence of apoptosis was assessed by examining cytospin preparations and the appearance of hypodiploid DNA in the flow cytometer. Culture supernatants were analyzed for GM-CSF, IL-1beta, and TNF-alpha by ELISA.

RESULTS

TSST-1, in a concentration-dependent manner starting at 0.1 pg/mL, significantly inhibited monocyte apoptosis and resulted in the production of the prosurvival cytokines GM-CSF, IL-1beta, and TNF-alpha. In coculture conditions with conditioned media from TSST-1-stimulated monocytes, with or without neutralizing antibody to the various cytokines, the data show GM-CSF production was responsible for the inhibition of apoptosis.

CONCLUSIONS

The data strongly suggest that staphylococcal exotoxins known to colonize skin lesions on patients with chronic AD may induce the production of GM-CSF, resulting in inhibition of monocyte-macrophage apoptosis, and thereby contribute to the chronicity of this inflammatory disease.

Reduced plasma c-AMP levels in children with atopic dermatitis

Plasma levels of cAMP and serum concentrations of IgE have been determined in children with acute atopic dermatitis (AD) and in a healthy control group, to illuminate the pathophysiological mechanisms that cause AD. There were significantly lower plasma levels of cAMP (P < 0.001) and significantly higher levels of serum IgE (P < 0.004) in children with AD, in comparison with a healthy control group. It is possible that defective control of c-AMP levels could contribute to the immunopathogenesis of AD and monitoring levels may be of value in the clinical evaluation of the disease.

Immunopharmacology of human mast cells and basophils

Human mast cells and basophils play a key role in the pathogenesis of several immunological and inflammatory disorders, not only by producing inflammatory and fibrogenic mediators, but also by directly (CD40 ligand) and indirectly secreting various cytokines and chemokines. Studies carried out to evaluate the effects of drugs that modulate the release of mediators and cytokines from these cells have contributed to clarifying the biochemical mechanism by which immunological and non-immunological stimuli activate these cells. Significant differences have been documented between human mast cells and basophils as regard the pharmacological agents that modulate the release of mediators, between mast cells isolated from different anatomical sites, and between compounds of the same class of drugs. Efforts to gain insight into the biochemical events occurring during immunological activation of mast cells and basophils could lead to the identification of new biochemical targets for therapeutic interventions in several immunological disorders.

The profile of the cytokines secreted during the generation of T-helper cells from atopic asthmatic subjects

This study investigated cytokine release by T-cell lines from atopic and nonatopic individuals in the presence of specific aeroallergen. Cell lines from atopic and nonatopic individuals secreted IL-2 for less than 14 and more than 21 days, respectively. All of the atopic, but not the nonatopic, cell lines exhibited a biphasic peak in IL-4 and IL-5 secretion. Flow cytometry revealed that, after 35 days, 89.3% of the atopic cells were T helpers and 73.2% were activated. Only 7.4% of the nonatopic cells displayed activation markers. In conclusion, T-cell differentiation may be controlled by other factors in addition to stimulation by aeroallergens.

Phosphodiesterase profile of human B lymphocytes from normal and atopic donors and the effects of PDE inhibition on B cell proliferation

1. CD19+ B lymphocytes were purified from the peripheral blood of normal and atopic subjects to analyse and compare the phosphodiesterase (PDE) activity profile, PDE mRNA expression and the importance of PDE activity for the regulation of B cell function. 2. The majority of cyclic AMP hydrolyzing activity of human B cells was cytosolic PDE4, followed by cytosolic PDE7-like activity; marginal PDE3 activity was found only in the particulate B cell fraction. PDE1, PDE2 and PDE5 activities were not detected. 3. By cDNA-PCR analysis mRNA of the PDE4 subtypes A, B (splice variant PDE4B2) and D were detected. In addition, a weak signal for PDE3A was found. 4. No differences in PDE activities or mRNA expression of PDE subtypes were found in B cells from either normal or atopic subjects. 5. Stimulation of B lymphocytes with the polyclonal stimulus lipopolysaccharide (LPS) induced a proliferative response in a time- and concentration-dependent manner, which was increased in the presence of interleukin-4 (IL-4). PDE4 inhibitors (rolipram, piclamilast) led to an increase in the cellular cyclic AMP concentration and to an augmentation of proliferation, whereas a PDE3 inhibitor (motapizone) was ineffective, which is in accordance with the PDE profile found. The proliferation enhancing effect of the PDE4 inhibitors was partly mimicked by the cyclic AMP analogues dibutyryl (db) cyclic AMP and 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole-3',5'-cyclic monophosphorothioate, Sp-isomer (dcl-cBIMPS), respectively. However, at concentrations exceeding 100 microM db-cyclic AMP suppressed B lymphocyte proliferation, probably as a result of cytotoxicity. Prostaglandin E2 (PGE2, 1 microM) and forskolin (10 microM) did not affect B cell proliferation, even when given in combination with rolipram. 6. Inhibition of protein kinase A (PKA) by differentially acting selective inhibitors (KT 5720, Rp-8-Br-cyclic AMPS) decreased the proliferative response of control cells and reversed the proliferation enhancing effects of rolipram. 7. Importantly, PDE4 activity in LPS/IL-4-activated B lymphocytes decreased by about 50% compared to unstimulated control values. 8. We conclude that an increase in cyclic AMP, mediated by down-regulation of PDE4 activity, is involved in the stimulation of B cell proliferation in response to LPS/IL-4. B cell proliferation in response to a mitogenic stimulus can be further enhanced by pharmacological elevation of cyclic AMP.

Modulation of Th1- and Th2-like cytokine production from mitogen-stimulated human peripheral blood mononuclear cells by phosphodiesterase inhibitors

1. Effects of phosphodiesterase (PDE) inhibitors on the production of IFN-gamma, IL-2, IL-4 and IL-5 by phytohemagglutinin (PHA)-stimulated human peripheral blood mononuclear cells (PBMC) were investigated. In addition, we investigated the effects of dibutyrylcyclic AMP (dbcAMP) and a beta-adrenoceptor agonist on production of these cytokines. 2. Type IV, type III and nonselective PDE inhibitors were effective at inhibiting the production of IFN-gamma and IL-2 production in a dose-dependent manner. In contrast, IL-4 and IL-5 production was inhibited by only the highest concentration of type IV inhibitor, and other agents had no effect on the production. 3. Similarly, dbcAMP inhibited the production of IFN-gamma and IL-2 more potently than IL-4 and IL-5. 4. The addition of a beta-adrenoceptor agonist increased the inhibitory effect of PDE inhibitors tested on the production of IFN-gamma and IL-2. 5. These results indicate that PDE inhibitors or cAMP-elevating agents modulate Th1 cytokine more effectively than Th2 cytokine production.

Regulation of interleukin-13 by type 4 cyclic nucleotide phosphodiesterase (PDE) inhibitors in allergen-specific human T lymphocyte clones

Interleukin-13 (IL-13) is a proinflammatory cytokine of T cell origin. Structural and functional studies suggest a key role for IL-13 in the genesis of chronic allergic inflammation; as such, its pharmacologic inhibition is of potential clinical utility. We studied the pharmacologic regulation of IL-13 expression by cyclic nucleotide phosphodiesterase (PDE) inhibitors in a panel of Amb a 1 (a major allergen of short ragweed, Ambrosia artemisiifolia)-specific T cell clones derived from a ragweed allergic, asthmatic subject. Proliferative responses of these cells were down-regulated by rolipram, a PDE4 inhibitor (% inhibitionMAX = 67%; IC50 = 20 microM). While the PDE3 inhibitor siguazodan provided no independent efficacy (IC50 > 10(-4) M), an increased efficacy of rolipram in the presence of 10(-5) M siguazodan was noted at 10(-6), 10(-5), and 10(-4) M rolipram (P < 0.03, 0.01, and 0.04, respectively). The EC50 values remained unchanged between assays using the PDE4 inhibitor with or without the PDE3 inhibitor. Both IL-13 gene expression and protein secretion into culture supernatants were down-regulated by the PDE4 inhibitor (P < or = 0.005). Once again, the use of a PDE3 inhibitor provided no independent efficacy (P > or = 0.2), and in this instance, increased efficacy of the PDE4 inhibitor with the PDE3 inhibitor was not apparent (P > or = 0.3). IL-13 production from clones with Th0, Th1, and Th2 phenotypes appeared equally sensitive to treatment with the PDE4 inhibitor. We conclude that the anti-inflammatory effects of PDE4 inhibitors may be mediated, in part, by down-regulation of IL-13.

Differential efficacy of lymphocyte- and monocyte-selective pretreatment with a type 4 phosphodiesterase inhibitor on antigen-driven proliferation and cytokine gene expression

Elevations of intracellular cyclic AMP, achieved with the use of phosphodiesterase (PDE) inhibitors, cause functional downregulation of most inflammatory cells. Rolipram, an inhibitor selective for the PDE4 isozyme, can markedly downregulate antigen-driven proliferation and cytokine gene expression of unfractionated human peripheral blood mononuclear cells. However, it is unclear whether PDE4 inhibitors in a mixed-cell system exert their immunosuppressive effect on the lymphocyte or on the monocyte fraction. We have used an adherence-based protocol for separating peripheral blood mononuclear cells, isolated from atopic individuals, into lymphocyte and monocyte fractions and have selectively treated these populations with rolipram prior to reconstituting the cell cultures to their original lymphocyte/monocyte proportions. Cellular responses to both ragweed and tetanus toxoid were analyzed for both proliferation and gene expression of proinflammatory cytokines. A dose-dependent downregulation of ragweed- and tetanus toxoid-driven proliferative responses was achieved by pretreatment of lymphocytes from peripheral blood with rolipram. This downregulation was significantly greater than that achieved with pretreatment of monocytes. Pretreatment of both populations failed to show synergistic downregulation of proliferation. Lymphocyte pretreatment with rolipram also resulted in marked downregulation of gene expression for IL-4, IL-5, and interferon-gamma compared to monocyte pretreatment in both ragweed- and tetanus toxoid-driven systems. Interestingly, monocyte pretreatment in these systems resulted in significant downregulation of IL-2 gene expression compared to lymphocyte pretreatment. Flow cytometric analysis failed to show alterations in any of a panel of surface activation and signal transducing molecules by rolipram treatment with or without antigen stimulation. We conclude that, in a mixed cell system, PDE4 inhibitors downregulate antigen-driven proliferation and gene expression of proinflammatory cytokines predominantly through their effects on lymphocytes rather than monocytes.

Effects of theophylline and rolipram on leukotriene C4 (LTC4) synthesis and chemotaxis of human eosinophils from normal and atopic subjects

1. The effects of the non-selective phosphodiesterase (PDE) inhibitor theophylline and the selective PDE4 inhibitor rolipram on leukotriene C4 (LTC4) synthesis and chemotaxis of complement 5a (C5a)- and platelet-activating factor (PAF)-stimulated human eosinophils obtained from normal and atopic donors were investigated. 2. Eosinophils were purified from peripheral venous blood of normal and atopic subjects by an immunomagnetic procedure to a purity > 99%. Eosinophils were stimulated with PAF (0.1 microM) or C5a 0.1 microM for 15 min and LTC4 was measured by radioimmunoassay (RIA). Eosinophil chemotaxis in response to PAF and C5a was assessed with 48-well microchambers (Boyden). 3. Under these conditions substantial amounts of LTC4 (about 300-1000 pg per 10(6) cells) were only detectable in the presence of indomethacin (0.1-10 microM). To explain this finding it was hypothesized that indomethacin reversed the inhibition of LTC4 synthesis by endogenously synthesized prostaglandins, in particular prostaglandin E2 (PGE2). In fact, eosinophils release 23 pg PGE2 per 10(6) cells following PAF stimulation; this PGE2 synthesis was completely inhibited by indomethacin and readdition of PGE2 inhibited eosinophil LTC4 synthesis (IC50 = 3 nM). The following experiments were performed in the presence of 10 microM indomethacin. 4. Theophylline (IC50 approximately 50 microM) and rolipram (IC50 approximately 0.03-0.2 microM) suppressed PAF- and C5a-stimulated LTC4 synthesis. This PDE inhibitor-induced suppression of LTC4 generation is mediated by activation of protein kinase A, since it was reversed by the protein kinase A inhibitor Rp-8-Br-cyclic AMPS. In addition, exogenous arachidonic acid concentration-dependently (0.3 microM-3 microM) reversed the inhibition of LTC4 synthesis by the PDE inhibitors, indicating that theophylline and rolipram suppress the mobilization of arachidonic acid. The beta 2-adrenoceptor agonist salbutamol inhibited eosinophil LTC4 synthesis (IC50 = 0.08 microM). The combination of salbutamol with theophylline (10 microM) or rolipram (3 nM) appeared to be additive. 5. Theophylline (IC50 approximately 40 microM), rolipram (IC50 approximately 0.02 microM [C5a], approximately 0.6 microM [PAF]) and PGE2 (IC50 approximately 3 nM) inhibited C5a- and PAF-stimulated eosinophil chemotaxis. The combination of PGE2 with theophylline resulted in an additive effect. 6. Both C5a- and PAF-stimulated eosinophil chemotaxis and LTC4 generation were significantly elevated in eosinophils from atopic individuals compared to normal subjects. However, eosinophils from normal and atopic individuals were not different with respect to their total cyclic AMP-PDE and PDE4 isoenzyme activities as well as the potencies of theophylline and rolipram to suppress LTC4 generation and chemotaxis.

The spectrum of cutaneous patch-test reactions in patients with atopic dermatitis

We have outlined rationale and problems associated with three types of patch tests that may provide diagnostic help in patients with difficult-to-manage AD. Each of these methods is imperfect and in need of greater study using a critical approach, better techniques, more attention to irritant controls, and better definition of atopic populations. Proof of validity for aeroallergen patch testing will necessarily require large quantities of purified antigens. In spite of all these problems, patch testing can be useful and sometimes essential for the diagnosis and management of difficult AD.

Abnormal IL-4 gene expression by atopic dermatitis T lymphocytes is reflected in altered nuclear protein interactions with IL-4 transcriptional regulatory element

Among the atopic disease, atopic dermatitis is characterized by the highest levels of serum IgE and by increased peripheral blood T-cell interleukin-4 (IL-4) production. IL-4 promotes IgE synthesis by B cells and stimulates the growth of IL-4-producing T cells and may contribute to the pathogenesis of this disease. In this study, in situ hybridization established that atopic dermatitis patients have a higher frequency of IL-4-producing peripheral blood T cell when compared to normal subjects. These in vivo-derived T cells were used to examine the signaling requirements of IL-4 production and the nuclear factors that associate with a critical IL-4 transcriptional regulatory element between -88 and -60 relative to the IL-4 transcription initiation site, the activation responsive element. We demonstrate that, as in T-cell lines, proteins belonging to the NF-AT and AP-1 family of transcription factors are present in stimulated cell extracts and specifically associate with the activation responsive element. Dysregulated IL-4 production is reflected in the nuclear proteins that associated this element. Using gel shift assays, we found that 12 of 12 nuclear extracts from stimulated atopic T cells formed the activation-dependent protein-DNA complex, compared to only 2 of 12 normal T-cell extracts. Activation complex formation correlated with the relative level of IL-4 mRNA and protein produced in stimulated T cells, suggesting that abnormal IL-4 gene expression in atopic disease may be linked to alterations in nuclear protein interactions with these promoter elements.

Phosphodiesterase inhibitors suppress proliferation of peripheral blood mononuclear cells and interleukin-4 and -5 secretion by human T-helper type 2 cells

It has been suggested that interleukin-4 and -5 (IL-4 and IL-5) are instrumental in the control of allergic disease. Elevated levels of IL-4 messenger RNA (mRNA) have been detected in numerous foci of atopic activity, including bronchoalveolar lavage (BAL) fluid from atopic asthmatics and skin of atopic dermatitis patients. IL-5 is important in eosinophil activation, which is a common feature of atopic disease. IL-5 mRNA has been detected in BAL fluid from both atopic and non-atopic asthmatics, indicating that IL-5 may be a common feature of the two disease states. Production of IL-4 and IL-5 by T cells appears to be associated with a high affinity cyclic AMP (cAMP) phosphodiesterase (PDE). This study was designed to compare the effects of PDE inhibitors Ro20-1724 and theophylline on (1) the mitogenic response of peripheral blood mononuclear cells from atopic and non-atopic individuals and (2) secretion of IL-4 and IL-5 by TH(2) cells after activation with PMA and anti-CD3. Both Ro20-1724 and theophylline inhibited proliferation of PBMC in a dose-dependent manner. There was no significant difference between proliferation of PBMC from atopic versus non-atopic donors, but Ro20-1724, a specific PDE IV inhibitor, was more potent at a concentration of 10(-5)M than theophylline in suppressing lymphocyte proliferation. Similarly, both PDE inhibitors suppressed secretion of IL-4 and IL-5 from TH(2)-like cell lines in a dose-dependent manner. In conclusion, as Ro20-1724 and theophylline inhibit proliferation of PBMC and secretion of IL-4 and IL-5 from human TH(2) cell lines, the development of a selective cyclic nucleotide PDE IV inhibitor may provide a promising new approach for asthma prophylaxis.

Allergic and irritant patch test reactions and atopic disease

This study presents a profile of patients with chronic recalcitrant eczematous disease referred by dermatologists for contact allergy evaluation. Allergic contact dermatitis (ACD) and irritant responses were carefully defined, as was the presence or absence of atopy obtained by history. Of 410 patients studied, 44% had no history of atopic disease and 46% were classed as definitely atopic. Among relevant ACD patch test reactors (n = 198), 51.5% had atopy, compared with 40.9% with no atopy but this difference was not significant. Likewise, among atopics (n = 189), 54% had definite, relevant ACD patch test responses while 33.9% had negative ACD (again not significant). Significance was seen in the higher mean number of positive allergic patch tests in the atopic group (2.7 versus 2.0, p = 0.0223). Irritant patch tests were highest among patients with both ACD and atopy (p = 0.0308) and the proportion of irritant responses correlated with increasing numbers of positive ACD tests. We conclude that atopics are at least as likely to have ACD as are non-atopics. Irritancy is increased in these patients with chronic dermatitis and the frequency of irritant reactions correlates with both greater numbers of ACD responses and with presence of atopy.

Prostaglandin E2 control of T cell cytokine production is functionally related to the reduced lymphocyte proliferation in atopic dermatitis

Past studies of peripheral blood mononuclear cells (PBMC) from patients with atopic dermatitis (AD) have demonstrated reduced proliferation. We have studied phytohemagglutinin-induced lymphocyte proliferation in the context of interleukin-4 (IL-4), interferon-gamma (IFN-gamma), and prostaglandin E2 (PGE2) production in cultures of PBMC from patients without and with AD. The proliferation index was found to correlate proportionally to IFN-gamma production and inversely to T-cell IL-4 and monocyte PGE2 production. Assays in parallel cultures showed significantly increased PGE2 production by purified AD monocytes. The proliferation index in PBMC from persons with AD was significantly reduced compared with normal PBMC. This difference was normalized in the presence of extrinsic IFN-gamma but exaggerated when IL-4 was added. Increased AD monocyte production of inflammatory factors (e.g., PGE2) and cytokines appears to increase IL-4 production by Th2 while suppressing IFN-gamma production by Th1. Restoration of the normal proliferation of PBMC by the addition of IFN-gamma may represent one mechanism for the clinical efficacy of IFN-gamma treatment of AD.

Emetic, central nervous system, and pulmonary activities of rolipram in the dog

Rolipram was characterized for its emetic, behavioral, cardiovascular and pulmonary activities in dogs, to assess its systemic pharmacology and potential bronchodilatory selectivity. At doses > or = 0.1 mg/kg i.v., rolipram induced emesis, anxiety, and stepping behaviors in conscious dogs, and increased heart rate and cardiac contractility in anesthetized instrumented dogs not treated with a beta-adrenoceptor antagonist. Cardiovascular effects in anesthetized dogs were apparently related to rolipram's central nervous system activities, in that they were associated with a reversal pentobarbital-induced anesthesia and could be ablated by pentobarbital supplementation. Rolipram's reversal of anesthesia was confirmed in uninstrumented dogs, where rolipram shortened pentobarbital sleep time while increasing heart and respiratory rates. After intragastric administration, rolipram exhibited greater emetic potency (100% emesis at 0.1 mg/kg p.o.) and lesser bronchodilatory potency (ED50 = 0.04 mg/kg i.d.) than after i.v. administration. The data demonstrate that rolipram is a potent bronchodilator that produces central nervous system effects only at higher doses when administered i.v. to the dog. Administered intragastrically, however, the bronchodilatory selectivity of rolipram is reduced presumably as a result of the activation of emetic reflexes at sites within the gastrointestinal tract.